This invention is generally directed to toner and developer compositions, and, more specifically, the present invention is directed to toner compositions and processes for the preparation of toner compositions. In one embodiment, there are provided in accordance with the present invention in situ processes for the preparation of toner compositions with average volume particle sizes equal to, or less than about 10 micrometers in embodiments without resorting to classification. The resulting toners can be selected for known electrophotographic imaging and printing processes, including color processes, and lithography. In an embodiment, the present invention is directed to a process for preparing a toner comprised of composite particles comprised of primary particles comprised of a nonpolar copolymer resin, secondary particles comprised of a pigment, wherein the secondary particles reside substantially on the surface of the primary particles and wherein the composite particles may have chemically modified outer surfaces and an average diameter of about 1 to 10 micrometers. In embodiments, the process of the present invention comprises preparing a latex emulsion by agitating a mixture of nonpolar olefins such as styrene and butadiene in an aqueous medium containing a mixture of nonionic and anionic surfactants, a chain transfer agent and a free radical initiator, and polymerizing the mixture by heating to form nonpolar olefinic resin particles in water comprised of, for example, poly(styrene-butadiene); thereafter adding and dispersing pigment particles with the nonpolar olefinic resin particles and flocculating the mixture by the addition of a cationic surfactant; homogenizing the flocculated mixture to form statically bound resin and pigment particle aggregates of from less than about 5 micrometers; heating and thereby fusing the pigment and resin particle aggregate mixture to form composite nonpolar toner sized particles of from about 3 to about 10 micrometers; optionally, chemically modifying the toner surface with, for example, chlorine gas to transform the olefinic resin present on the outer surface of the composite toner particle to, for example, a chlorinated poly(styrene butadiene) species poly(styrene-butadiene-dichloro butene); and isolating the toner particles by concentrating, washing and drying. The toner and developer compositions of the present invention can be selected for electrophotographic, especially xerographic imaging and printing processes, including color processes.
In reprographic technologies, such as xerographic and ionographic devices, toners with small average volume diameter particle sizes of from about 5 microns to about 20 microns are utilized. Moreover, in some xerographic technologies, such as the high volume Xerox Corporation 5090.TM. copier-duplicator, high resolution characteristics and low image noise are highly desired, and can be readily attained utilizing small sized toners with average volume particle of less than 11 microns and preferably less than about 7 microns and with narrow geometric size distribution (GSD) of less than about 1.6, preferably less than about 1.4, and more preferably less than about 1.3. Additionally, in some xerographic systems wherein process color is required such as pictorial color applications, small particle size colored toners of less than 9 microns and preferably less than about 7 microns are highly desired to avoid paper curling. Paper curling is especially observed in pictorial or process color applications wherein three to four layers of toners are transferred and fused onto paper. During the fusing step, moisture is driven off from the paper due to the high fusing temperatures of from about 130 to 160 degrees centigrade applied to the paper from the fuser. Where only one layer of toner is present such as in black or highlight xerographic applications, the amount of moisture driven off during fusing is re-absorbed proportionally by paper and the resulting print remains relatively flat with minimal curl. In pictorial color process applications wherein three to four colored toner layers are present, a thicker toner plastic level present after the fusing step inhibits the paper from sufficiently absorbing the moisture lost during the fusing step, and image paper curling results. Since surface area of particle size is inversely proportional to particle size, it is preferable to use small toner particle sizes of less than 9 microns and preferably less than about 7 microns and with higher pigment loading such that the mass of toner layers deposited onto paper is reduced to obtain the same quality of image and resulting in a thinner plastic toner layer onto paper after fusing, and hence, minimizing or avoiding paper curling. Toners prepared in the instant invention with lower fusing temperatures such as from about 100 to about 140 degrees centigrade help to avoid paper curl. Lower fusing temperatures minimizes the loss of moisture from paper, thereby reducing or eliminating paper curl. Furthermore, in process color applications and especially in pictorial color applications, high gloss is necessary, as well as high projection efficiency properties with transparency images.
Numerous processes are known for the preparation of toners, such as, for example, conventional processes wherein a resin is melt kneaded or extruded with a pigment, micronized and pulverized to provide toner particles with an average volume particle diameter of from about 7 microns to about 20 microns and with broad geometric size distribution of from about 1.4 to about 1.7. In such processes it is usually necessary to subject the aforementioned toners to a classification procedure such that the geometric size distribution of from about 1.2 to about 1.6 are attained. However, in the aforementioned conventional process, low toner yields after classifications may be obtained and dependent on the average volume particle sizes of said toner. Generally, during the preparation of toners with average particle size diameters of from about 11 microns to about 15 microns, toner yields range from about 70 percent to about 85 percent after classification. Additionally, during the preparation of smaller sized toners with particle sizes of from about 7 microns to about 11 microns, lower toner yields are obtained after classification, such as from about 50 percent to about 70 percent. With the processes of the present invention in embodiments, small average particle sizes of from about 3 microns to about 9, and preferably 7 microns are attained without resorting to classification processes, and wherein high toner yields are attained such as from about 90 percent to about 98 percent in embodiments. Additionally, toners prepared by conventional processes must not readily aggregate or block during manufacturing, transport or storage prior to use in electrophotographic systems and must exhibit low temperature fusing properties in order to minimize fuser energy requirements. Accordingly, conventional toner resins are restricted to having exhibit glass transition temperatures of greater than about 55 degrees centigrade and preferably of about 60 degrees centigrade to satify caking or blocking requirements. Toner caking or blocking is known in the art and refers to the minimum temperature necessary for toner aggregation to occur over an extended period of time, such as from about 24 hours to 48 hours. The caking or blocking temperature requirement of a toner should be greater than about 55 degrees centigrade and preferably greater than about 60 degrees centigrade, in order to avoid toner aggregation in storage or use prior to fixing a powdered toner image to a receiver sheet. This blocking requirement restricts the toner fusing properties of from about 135 degrees centigrade to about 160 degrees centigrade. In process color or pictorial applications, wherein low paper curl is a requirement, low toner fusing properties are desired such as less than about 140 degrees centigrade and preferably less than 110 degrees centigrade such that moisture evaporation or removal from paper is minimized or preferably avoided. With the toners of this invention, the toners fuse at lower temperatures than conventional toners, such as from about 110 to about 150 degrees centigrade, thereby reducing the energy requirements of the fuser and more importantly resulting in lower moisture driven off from the paper during fusing, and hence lowering or minimizing paper curling. For the toners of this invention, the blocking and fusing properties of the toners are disintegrated by the chemical surface process of halogenating the toner surface. During the process for the preparation of the toner of this invention, the polymerized primary emulsion resin such as poly (styrene-butadiene) exhibits a glass transition temperature of from about 40 degrees centigrade to about 50 degrees centigrade and thermal properties amenable to achieve the low fusing properties such as from about 110 degrees centigrade to about 140 degrees centigrade, and after a flocculation and aggregation fusing process and during, for example, the chlorination step, the outer surface of the toner resin surface is chemically transformed from poly(styrene-butadiene) to chlorinated poly(styrene-butadiene) such that the outer surface of the toner resin composite has a glass transition of from about 55 degrees centigrade to about 60 degrees centigrade necessary for the blocking requirement. This latter chemical surface treatment step allows one to separate toner blocking requirements from fusing requirements and results in low fusing toners of from about 110 degrees centigrade to about 140 degrees centigrade which are necessary to minimize or eliminate paper curling. That is by lowering the fusing temperature range to about 100.degree. to 140.degree. C. a reduction or elimination in paper curl is achieved. In addition, by the toner particle preparation process of this invention, small particle size toners of from about 3 microns to about 7 microns are prepared with high yields as from about 90 percent to about 98 percent by weight of all toner starting material ingredients.
Additionally, other processes such as and including encapsulation, coagulation, coalescence, suspension polymerization, or semi-suspension and the like, are known, wherein the toners are obtained by in situ one pot methods. Moreover, encapsulated toners are known wherein a core comprised of pigment and resin is encapsulated by a shell, and wherein the toner melt rheological properties are separated wherein a core material provides low fusing properties such as from about 100 to 125 degrees centigrade, and an encapsulating shell provides necessary blocking properties for particle stability prior to fusing. However, it is known that encapsulated toners do not provide high gloss due to high surface tension, high glass transition and high melting temperatures of the shell, and also result in poor projection efficiency due to the difference in refractive index between the shell and core resulting in light scattering. Other in situ toners prepared by suspension, coagulation, coalescence, are known, wherein the toners are comprised of substantially similar composition to conventional toners with, in some cases, having surfactants or surface additives on the toner surface prepared by various processes. Although, these latter aforementioned toners are amenable to high gloss, high projection efficiency, and small particle size toners, their fusing performances are restricted to the thermal properties of the toner, such as glass transition (Tg), in that the toners must satisfy blocking requirements and hence are restricted to glass transitions of above 55 degrees centigrade and therefore fusing temperatures of from about 135 to about 160 degrees centigrade, and have inferior paper curl properties for process color applications. By the processes of the instant invention, toner melt rheological properties are separated in that a chemical halogenation process increases the glass transition of the outer surface of the toner composite resin of from about 45 to 55 degrees centigrade to about 55 to 60 degrees centigrade, hence providing required blocking properties and low fusing temperatures of from about 110 degrees centigrade to about 140 degrees centigrade necessary for minimizing or avoiding paper curling.
In the embodiments of the instant invention a process for the preparation of a nonpolar composite particle toner composition is disclosed comprising the steps of: (i) preparing a latex emulsion by agitating in water a mixture of nonionic surfactant such as polyethylene glycol or polyoxyethylene glycol nonyl phenyl ether, an anionic surfactant such as sodium dodecyl sulfonate or sodium dodecyl benzenesulfonate, a first nonpolar olefinic monomer such as styrene, acrylate or methacrylate, a second nonionic nonpolar diolefinic monomer such as butadiene or isoprene; (ii) polymerizing the reaction mixture by heating from ambient temperature to about 80.degree. C. the olefinic and diolefinic monomers to nonpolar olefinic emulsion sized particles of from about 5 nanometers to about 500 nanometers in average volume diameter; (iii) diluting the nonpolar olefinic emulsion resin mixture with water from about 50% solids to about 15% solids; (iv) adding to the mixture a colorant or pigment particles of from about 3 percent to about 15 percent by weight of toner and optionally dispersing the resulting mixture by dispersing utilizing a Brinkman or IKA homogenizer; (v) adding a cationic surfactant such as dialkylbenzene dialkylammonium chloride and the like thereby effecting flocculation of the colorant or pigment particles with emulsion resin particles; (vi) homogenizing the flocculated resin-pigment mixture at from about 2000 to about 6000 revolution per minute to form high shear statically bound aggregate composite particles of less than about 5 microns in volume average diameter; (vii) heating the statically bound aggregate composite particles of from about 60 degrees centigrade to about 95 degrees centigrade and for a duration of about 60 minutes to about 600 minutes to form nonpolar toner sized particles of from about 3 microns to about 9 microns in volume average diameter; (viii) optionally halogenating the nonpolar toner sized particles with a halogen, for example, chlorine gas to chemically transform the nonpolar olefinic moieties of the resin present on the outer surface of the toner resin to chlorine containing hydrocarbon moieties; and (ix) isolating the nonpolar toner sized composite particles by washing, filtering and drying thereby providing a nonpolar composite particle toner composition. Flow additives to improve flow characteristics may then optionally be employed such as Aerosils or silicas, and the like, of from about 0.1 to about 10 percent by weight of the toner.
In a patentability search there is illustrated in U.S. Pat. No. 4,996,127 a toner of associated particles of secondary particles comprising primary particles of a polymer having acidic or basic polar groups and a coloring agent. The polymers selected for the toners of the '127 patent can be prepared by an emulsion polymerization method, see, for example, columns 4 and 5. In column 7 of the '127 patent it is indicated that the toner can be prepared by mixing the required amount of coloring agent and optional charge additive with an emulsion of the polymer having an acidic or basic polar group obtained by emulsion polymerization as indicated in column 3. Additionally, note column 9, line 50 to 55, wherein polar monomers such as acrylic acid in the emulsion resin is necessary, and note Comparative Example 1, column 9, lines 50 to 55 wherein toner preparation is not obtained without the use of a polar group such as acrylic acid. The present invention is directed to an improved process wherein the emulsion monomers or resultant resin particles do not contain acidic or basic groups, and toner particles are obtained without the use of polar acidic groups such as acrylic acid, thereby reducing toner humidity sensitivity. Additionally, with processes of the instant invention, halogenation, for example, chlorination of the outer surface of the composite particles provides an improvement in blocking characteristics, and hence enhances the minimum fix temperature of the toner.
Illustrated in U.S. Pat. No. 4,797,339, is a toner composition comprised of an inner layer comprising a resin ion complex having a coloring agent, a charge enhancing additive and pigment dispersed therein, and an outer layer containing a flowability imparting agent. Note column 2 and 3, wherein the ion complex resin is comprised of an acidic emulsion copolymer resin and basic emulsion resin comprised of styrene acrylates containing acidic or basic polar groups similar to the '127 patent.
U.S. Pat. No. 4,983,488 discloses a process for the preparation of toners by the polymerization of a polymerizable monomer dispersed by emulsification in the presence of a colorant and/or a magnetic powder to prepare a principal resin component and then effecting coagulation of the resulting polymerization liquid in such a manner that the particles in the liquid after coagulation have diameters suitable for a toner. It is indicated in column 9 of this patent that coagulated particles of 1 to 100 micrometers in diameter, and particularly 3 to 70 micrometers in diameter, are obtained. It is also indicated in column 4, lines 60 to 65, that the glass transition of the emulsion resin should be above 50 degrees centigrade, and when the glass transition is too low, caking resistance, that is resistance to blocking, tends to decrease and if the glass transition is too high the fixing property tends to be poor. The toners of the instant invention differ from the reference toners in that the process is simple and does not utilize coagulating agents. Moreover, emulsion resins with relatively lower glass transition of about 40 to 45 degrees centigrade are used, and resistance to caking is avoided by the halogenation process of the toner surface wherein the glass transition is raised to about 50 to about 55 degrees centigrade, hence caking, blocking or undesired aggregation of toner particles is avoided and low fixing temperatures are maintained as well as excellent triboelectric characteristics, high gloss, and low humidity sensitivity.
Copending application U.S. Ser. No. 07/767,454, filed Sep. 30, 1991, the disclosure of which is totally incorporated herein by reference, discloses an in situ suspension process for a toner comprised of a core comprised of a resin, pigment and optionally charge control agent and coated thereover with a cellulosic material. Another patent of interest is copending U.S. Ser. No. 07/695,880, filed May 6, 1991 entitled `Toner Compositions`, the disclosure of which is totally incorporated herein by reference, discloses low melt toner particles prepared by conventional comminution processes that are halogenated to form encapsulated toner particles with a higher melting halopolymer shell.
Additionally, U.S. Pat. No. 4,876,313, discloses an improved core and shell polymers having an alkali-insoluble core and an alkali-soluble shell which polymers are prepared by emulsion polymerization of the core-shell polymers utilizing compounds which chemically graft the core and shell polymers together.
Documents disclosing toner compositions with charge control additives include U.S. Pat. Nos. 3,944,493; 4,007,293; 4,079,014; 4,394,430; and 4,560,635 which illustrates a toner with a distearyl dimethyl ammonium methyl sulfate charge additive. These toners are prepared, for example, by the usual known jetting, micronization, and classification processes. Toners obtained with these processes generally possess a toner volume average diameter of form between about 10 to about 20 microns and are obtained in yields of from about 85 percent to about 98 percent by weight of starting materials without classification procedure.
There is a need for black or colored toners wherein small particle sizes of less than or equal to 7 microns in volume diameter. Furthermore, there is a need for colored toner processes wherein the toner synthetic yields are high, such as from about 90 percent to about 100 percent while avoiding or without resorting to classification procedures. In addition, there is also a need for black and colored toners that are non-blocking, such as from about 55 to about 60 degrees centigrade, of excellent image resolution, non-smearing and of excellent triboelectric charging characteristics. Moreover, there is a need for black or colored toners with: low fusing temperatures, of from about 110 degrees centigrade to about 150 degrees centigrade; of high gloss properties such as from about 50 gloss units to about 85 gloss units; of high projection efficiency, such as from about 75 percent to about 95 percent efficiency or more, and result in minimal or no paper curl.